Technical Field
The invention concerns a level device, in particular for a spirit level, having the features discussed below.
The invention also concerns a spirit level having at least one such level device and a process for the production of such a level device.
Level devices are required for a large number of measuring instruments, including spirit levels, laser measuring devices, tripods and the like. Level devices are nowadays mostly made from plastic material and have a substantially cylindrical cavity for receiving a level liquid and a marking body which is generally in the form of an air bubble. The leveling position of the level device is so determined that the marking body comes to lie between two markings which are generally provided at the inside of the cavity accommodating the liquid. The cavity is generally of a barrel-shaped basic shape so that the marking body assumes a stable position in the leveling operation.
Background Art
Attempts are known from the state of the art to improve the readability of the level device and thus the degree of accuracy in determining the leveling position.
German laid-open specification DE 1914699 discloses a level device comprising a plastic body, wherein at least one of the surfaces of the plastic body is curved. In that arrangement that curvature of the surface is kept of a lens-shaped configuration and there is a curvature both in the longitudinal direction and also in the transverse direction. In that case the level device body containing the cavity is of a cuboidal configuration and the lens-shaped portions are formed by way of additional material at the side surfaces of the cuboidal level device body. The curvature on the cuboidal plastic body is in the form of a portion of a circular arc, both in the longitudinal direction and also in the transverse direction. The radius of the lens-shaped portion in the longitudinal direction approximately corresponds to 2.5 times length and the radius of the lens-shaped portion in the transverse direction approximately corresponds to 1.17 times the width of the cuboid. In that way the aim is to achieve an optical magnification, in particular of the marking lines and the marking body, in the region of the cavity.
British patent specification GB 1210449 teaches a level device for a spirit level comprising a transparent level device body which includes a cavity for receiving the level device liquid and the marking body, wherein the wall thickness of the level device body is of a lens-shaped configuration to achieve a magnification effect. Disadvantages here are the low degree of optical magnification which can be achieved and the depression which occurs in the installation position in the spirit level.
The proposals disclosed in the state of the art for improved readability or for optical magnification of the marking body however can only be applied to so-called horizontal level devices, or they suffer from disadvantages in use when applied to vertical level devices.
Horizontal level devices are level devices having a substantially cuboidal level device body, which are used to determine the horizontal position in spirit levels. In the installation position, for example in a spirit level, the level device body forms with three of its outside surfaces the boundary surface which faces outwardly, that is to say that arrangement does not involve any enclosure of the level device body in a further transparent body.
To determine the vertical position in spirit levels, so-called vertical level devices, also referred to as round level devices or plumb level devices, are used. In vertical level devices the level device body is injection molded with an initially cylindrical or slightly conical cavity which is subsequently turned out in a barrel shape.
In contrast to horizontal level devices the level device body is arranged for use in a carrier body which extends around the level device body and has transparent covers. The carrier body is generally of a cylindrical basic shape but it can also be oval or cuboidal.
The viewing angle when reading off the vertical level device would be severely restricted if the generally cuboidal or barrel-shaped level device body were fitted alone, that is to say without an additional carrier body and in flush relationship, into the main body of the measuring means. For, in that case, in fact with shallow viewing angles, the edge of the recess into which the level device body is fitted into the measuring means is disposed in the field of view of the observer. A vertical level device is frequently read off in overhead operations, and for that reason great significance is attributed to that point.
Fitment of the generally cuboidal or barrel-shaped level device body into a markedly enlarged and for example round recess is disadvantageous as dirt can here pass into the recess.
That results in the need to offer vertical level devices in a carrier body and provided with covers.
That generally cylindrical carrier body comprises an annular body which forms the peripheral casing and two covers for closing the carrier body.
The production of vertical level devices with a box with plane-parallel covers is subject to restrictions. More specifically it has proven to be impracticable from the production engineering point of view for the vertical level device to be in the form of a solid injection molding, that is to say in one piece and without cavities. Implementation in the form of a solid injection molding would be suitable in the best-case scenario for very small level devices which in turn are difficult to read off. For, the thick-walled nature of the component means that so-called collapse depressions occur due to shrinkage, whereby the boundary surfaces which face outwardly in the installation condition, that is to say the cover surfaces of the cylindrical carrier body, are no longer plane-parallel and flat. Those deformations which lead to severe optical impairments can be corrected, if at all, only by complicated and expensive mechanical post-treatment.
The outside contour of the level device body can be cylindrical or cuboidal. A disadvantage with vertical level devices with cuboidal outside contours is that, when conducting reading-off operations which differ from the horizontal in relation to the level device which is disposed in the leveling position, the edges of the cuboidal outside contour interfere with the reading as the bubble appears duplicated due to refraction at the edge of the cuboidal outside contour.
Vertical level devices in accordance with the state of the art suffer from numerous disadvantages: they have edges at the level device body, by which the marking body appears optically divided or distorted. If the aim is to achieve a lens effect, they exhibit an outward curvature, that is to say in the installation situation in a spirit level, a depression or recess is always formed, in which dirt can be deposited.